How do you define bone disease progression in mCRPC while on docetaxel?

Defining bone scan progression on docetaxel is no different than in other treatment contexts and generally, I use PCWG2-3 criteria. I generally do not stop docetaxel in the first 4 cycles based on PSA changes alone since transient PSA rises followed by falls can occur during these first 3 months. However, radiographic soft tissue or bone scan progression or pain progression are good reasons to consider alternative treatments based on a patient no longer benefiting. Radiographic progression is more strongly associated with worse survival than PSA progression. I get scans every 3 months while on chemotherapy. If PSA keeps rising after 4 cycles, I may image more often or consider alternatives such as cabazitaxel, radium, or PSMA-Lu177 or a tri...